The discussion of any prior art documents, techniques, methods or apparatus is not to be taken to constitute any admission or evidence that such prior art forms, or ever formed, part of the common general knowledge.
Pumpable props are elongate hollow members that can be filled (pumped) with a settable material such as grout to form a strong load bearing column. It is known for these props to be length adjustable.
A known type of pumpable prop is described in international patent publication WO 2012/016272 by inventor Craig Douglas Barnett. This prop acts as a secondary roof support structure in an environment such as an underground mine.
It has been found that it may be desirable to top off a secondary roof support system, such as one embodiment of the previously described prop, with members such as pieces of timber which are interposed between the top of the prop and the mine ceiling. The use of timber members (or other suitable structures) in this manner will typically “soften” the support response due to the contact compatibility of the timbers with the uneven roof, requiring wedges or small pieces of wood to provide a tight fit. A desirable consequence of the softened support response is that roof convergence can then occur with minimal loss of integrity. In addition, poor construction practices, in which multiple timber layers are placed on top of the roof support system, may provide hinge points that can also reduce the overall stability of the support. When less than full secondary roof support system contact with the roof is achieved, the wood response alone can result in a softening response which delaminates the strata in the roof mine and, very undesirably, weakens its integrity.
It is an object of the present invention to address one or more of the above-described problems or to at least provide a useful alternative to those props and stays that have hitherto been known in the prior art.